Explicit Performance in Girls and Implicit Processing in Boys: A Simultaneous fNIRS-ERP Study on Second Language Syntactic Learning in Young Adolescents

Abstract

Learning a second language (L2) proceeds with individual approaches to proficiency in the language. Individual differences including sex, as well as working memory (WM) function appear to have strong effects on behavioral performance and cortical responses in L2 processing. Thus, by considering sex and WM capacity, we examined neural responses during L2 sentence processing as a function of L2 proficiency in young adolescents. In behavioral tests, girls significantly outperformed boys in L2 tests assessing proficiency and grammatical knowledge, and in a reading span test (RST) assessing WM capacity. Girls, but not boys, showed significant correlations between L2 tests and RST scores. Using functional near-infrared spectroscopy (fNIRS) and event-related potential (ERP) simultaneously, we measured cortical responses while participants listened to syntactically correct and incorrect sentences. ERP data revealed a grammaticality effect only in boys in the early time window (100-300 ms), implicated in phrase structure processing. In fNIRS data, while boys had significantly increased activation in the left prefrontal region implicated in syntactic processing, girls had increased activation in the posterior language-related region involved in phonology, semantics, and sentence processing with proficiency. Presumably, boys implicitly focused on rule-based syntactic processing, whereas girls made full use of linguistic knowledge and WM function. The present results provide important fundamental data for learning and teaching in L2 education.

Keywords: adaptive hemodynamic response function; phrase structure; proficiency; reading span test; sentence; sex differences; syntax; working memory.

FIGURE 1

Cortical projection points of fNIRS measurements and average β-values (response amplitudes) of the oxy-Hb and deoxy-Hb signals over 53 participants and three conditions as a function of peak latency τ_p. (A) Cortical projection points of fNIRS measurements (location of 22 channels on each hemisphere) are mapped onto the MNI standard brain coordinate system using spatial registration. (B) To examine the effects of τ_p, the average β-values over 53 participants and three conditions were calculated and compared for all τ_p ranges for 44 channels. Channel 16 in both the left and right hemispheres in the vicinity of auditory cortex were included among the channels within the top 10% β-values of 22 channels in each hemisphere. Therefore, τ_p was determined by averaging the τ_p values at the highest β-values of channel 16 in both hemispheres: optimal τ_p was 5 s for both oxy-Hb and deoxy-Hb signals.

FIGURE 2

Sex differences in behavioral responses. (A) Sex differences in grammar listening test (Grammar_L) scores. (B) Sex differences in RST scores. (C) Relationship between RST and Grammar_L scores for boys. (D) Relationship between RST and Grammar_L scores for girls. While there was no significant relationship between RST and Grammar_L scores for boys (C), there was a significant positive relationship between them for girls (D).

FIGURE 3

Grand-average ERPs at the onset of the second phrase. Five exploring electrodes were placed based on the international 10–20 system. Negative voltage is plotted up. Red lines denote the average amplitude for incorrect sentences and black lines denote that for correct sentences. Left: grand-average ERPs for boys; right: grand-average ERPs for girls.

FIGURE 4

Mean amplitude of each phase. The mean amplitudes of the five exploring electrodes are plotted for each phase. Left: mean amplitude for boys; right: mean amplitude for girls. Black bars denote amplitude for correct sentences. Red bars denote amplitude for incorrect sentences. Asterisks represent statistical significance in post hoc comparisons (^∗∗∗P < 0.005, ^∗∗P < 0.01, ^∗P < 0.05). Error bars indicate standard error.

FIGURE 5

Correlations between grammar listening test scores and cortical activation during correct-sentence processing [boys (A) and girls (B)] and incorrect-sentence processing [boys (C) and girls (D)]. Colored bars represent Pearson’s correlation coefficient. Asterisks depict channels that showed a significant correlation between test score and cortical activation after Bonferroni correction using the Dubey/Armitage-Parmar (D/AP) alpha boundary to take into account the spatial correlation of 44 measurement channels. We set the statistical threshold of fNIRS analysis at 0.005. In order to consider the spatial extent of cortical activation, we defined ROIs that consisted of single or multiple core channels which fulfilled the determined threshold (0.005) and adjacent channels that satisfied a secondary threshold of P < 0.05, which are depicted with plus signs. The average activation of the nearest-neighboring significant channels satisfying the above threshold was calculated for each ROI, and graphs showing the correlations between test score and cortical activation are displayed. The table at the bottom shows the statistical results of correlation analyses (Pearson’s correlation coefficients, r and P-values) for each ROI so that the trends of similarities and/or differences in the relationships between Grammar_L scores and cortical activation can be compared between sexes, as well as between correct- and incorrect-sentence conditions.

FIGURE 6

Results of partial correlation analyses between grammar listening test score and cortical activation during correct-sentence processing [boys (A) and girls (B)] and incorrect-sentence processing [boys (C) and girls (D)] with RST score (WM capacity) as a control variable. Colored bars represent partial correlation coefficient. Asterisks and plus signs are the same as those in Figure 5. In the table to the middle right side, statistical results of partial correlation analyses (partial correlation coefficients, r and P-values) are shown for each ROI so that the trends of similarities and/or differences in the relationships between Grammar_L scores and cortical activation can be compared between sexes, as well as between correct- and incorrect-sentence conditions.